The present invention relates to interface units for allowing digital communication between digital data devices employing different message protocols.
There are presently data communications devices in use today which require the data to be packed into specific message formats for reliable data transmission and reception. Examples of such devices are terminals which are employed for anti-jam secure radio transmission. There are different types of such terminals in use today, each adapted for communication of digital data in a specific message format. By way of example, the U.S. military employs a tactical radio system known as the "Joint Tactical Information Distribution System" (JTIDS) for tactical information exchange in an anti-jam secure link.
JTIDS employs a communication technique known as Time Division Multiple Access (TDMA) which permits messages to be sent from numerous terminals on a specified network in a time-sequenced basis. JTIDS is a jam resistant system using spread spectrum techniques and fast frequency hopping to distribute the transmitted data over a wide frequency bandwidth. Thus, JTIDS information is broadcast omnidirectionally at many thousands of bits per second and can be received by any JTIDS terminal within range. Information flows directly from many transmitters to many receivers; each JTIDS terminal can select or reject each message according to its need for the information.
The JTIDS may employ one particular data protocol known as Interim JTIDS Message Set "IJMS", or another protocol known as Tactical Digital Link "TADIL J", comprising an alphabet of types of data messages. For example, each IJMS message comprises a header word which defines the type of message, and eight data words containing the information. A single message might comprise information such as track report, fuel and ordinance reserves, position, and so on.
Other types of terminals also exist, with data protocols which do not coincide with those employed by JTIDS. Military examples include Army Tactical Datalink ATDL-1, TADIL A, and TADIL B. These terminals provide secure transmission capabilities, but are not adapted to provide significant jamming resistance. In many instances, it would be advantageous to allow communication between a JTIDS network and another tactical network such as TADIL B, so as to take advantage of an existing JTIDS network to provide a jamming resistance capability.
Thus, there exists a need to provide a means to allow communication between two or more types of communication terminals employing different message formats. Attempts have been made to meet this need by the provision of a translator terminal, which receives the information signal from one type of communication terminal employing one specific message format, and "translates" the intelligence from the terminal into a second type of message format compatible for utilization by the second user. The translation process is understood to involve the decoding of the information in one format, and subsequent encoding of the data into the second type of message format. Such translator devices are subject to translation losses or errors and are very expensive.
It would therefore be an advance in the art to provide an improved means for interfacing between data communications terminals employing different message protocols so as to allow communication between such terminals, without employing a data translator.